Tap 540- 4: Strange quarks



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TAP 540- 4: Strange quarks
An early classification of strange baryons by Murray Gell-Mann and Yuval Ne’emen gave this arrangement, called the baryon decuplet. The diagonal rows show baryons of the same charge. The Δ and Δ particles are more massive versions of the neutron and proton respectively


-




0




+




++

strangeness 0




-




0




+




strangeness -1







-




0







strangeness -2










-










strangeness -3

The - was, in fact, predicted by Gell-mann from a gap in this pattern in much the same way as Mendeleyev predicted missing elements from gaps in his table. The subsequent discovery of the - confirmed that particle physicists were on the right track with this classification, which led Gell-mann and Zweig to the quark theory.


The strange quark s is a more massive version of the down quark d, and has the same charge (-e/3).
The presence of a strange quark gives a baryon or meson a strangeness of -1.

1. The 0 and + particles are more massive versions of the neutron and proton respectively. Underneath each particle in the first row, write the three quarks that make up that baryon.

2. The strange quark s is a more massive version of the down quark d, and has the same charge (-e/3).How many strange quarks must there be in

(a) the  particles?

(b) the  particles?

(c) the  particle?


3. Write under all the strange baryons the three quarks they must contain.

The strange mesons fit a similar pattern:







K 0




K+




strangeness +1

-




0




+

strangeness 0




K -




K 0




strangeness -1

4. If the strange quark s has a strangeness of -1, what is the strangeness of its anti-quark, s-bar?

5. Each of these seven mesons consists of a u, d or s quark and a u-bar, d-bar or s-bar antiquark. Write down under each meson the quark and antiquark it contains.
Answers and worked solutions

An early classification of strange baryons by Murray Gell-Mann and Yuval Ne’emen gave this arrangement, called the baryon decuplet. The diagonal rows show baryons of the same charge. The 0 and + particles are more massive versions of the neutron and proton respectively.

1. and 3.


-

ddd





0

udd





+

uud





++

uuu

strangeness 0





-

dds





0

uds





+

uus




strangeness -1









-

dss





0

uss







strangeness -2












-

sss










strangeness -3


2.

(a) 1



(b) 2

(c) 3


4. +1

5.





K0

d s-bar





K+

u s-bar




strangeness +1





d u-bar





0

d d-bar


u u-bar

s-sbar





+

u d-bar

strangeness 0





K

s u-bar





K 0

s d-bar




strangeness -1




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